Tool and method for the chemical vapor deposition of a two-phase layer on a substrate member

ABSTRACT

The invention relates to a tool, especially a cutting tool, comprising a substrate member onto which at least one layer is deposited by means of CVD, and a method for the chemical vapor deposition of a two-phase layer on a sintered part. According to the invention, the single deposited layer or at least one of the layers is provided with a TiCN phase. TiOCN phase, TiOC phase, or TiC phase and an additional phase consisting of ZrO 2  and/or HfO 2 . CH 3 CN, C 5 H 5 N, or C 6 H 6  is used in the gas atmosphere for producing such a layer in addition to TiCl 4 , HfCl 4 , and/or ZrCl 4  and CO 2 . the remainder being composed of H 2  and/or Ar.

The invention relates to a tool, especially a cutting tool, comprised of a substrate body upon which a layer is deposited by CVD. The invention also relates to a method of CVD deposition of a two phase-layer on a substrate body.

Coated substrate bodies for use as cutting elements are basically known.

Thus, for example in German Patent Document 100 17 909 A1, substrate bodies on a tungsten carbide basis and provided with a hard coating are known which have a titanum composite layer with at least one coating of TiC, TiN, TiCN, TiCO and TiCNO and an Al₂O₃ and/or Al₂O₃—ZrO₂ composite layer. In the last mentioned case, ZrO₂ particles are dispersed in an Al₂O₃ phase. Furthermore, it is also known to provide layer sequences in the form of TiN—TiCN—TiN layers, optionally with an additional outer Al₂O₃ layer. Al₂O₃ layers which are deposited by means of a CVD process can, depending upon the process conditions, be in the form of α-Al₂O₃,κ-N₂O₃ or amorphous Al₂O₃. The German Patent Document DE 100 17 909 A1 discloses for the production of a TiCN layer, a CVD process in which at an average temperature range between 700° C. and 950° C., a reaction gas mixture is used which contains CH₃CN.

It is the object of the present invention to provide an improved tool and especially a cutting tool of the aforedescribed type that because of its coating has an improved life in dry machining as well as wet machining and especially in the turning of cast workpieces or heat treatable steels (CK45).

This object is achieved with the tool according to claim 1 which is characterized in accordance with the invention that the single deposited layer or at least one of the first layers, apart from a TiCN phase or a TiOCN phase or a TiC phase or a TiOC phase has a further comprised of ZrO₂ and HfO₂. This multiphase layer can be the single layer, an intermediate layer (a layer between two other layers) or an outer layer or coating, whereby, depending upon the use, the procedures can be varied based upon the consideration that with increasing ZrO₂ and/or HfO₂ proportions, the hardness of the respective layer drops.

Further features of the tool are described in the dependent claims.

Thus the mentioned further phase of ZrO₂ and HfO₂ can be present in a monoclinic and/or tetragonal form.

Upon the layer defined in claim 1, according to a further feature, an Al₂O₃ layer can also be deposited, preferably as an outer layer or coating and preferably also as an α-Al₂O₃layer. The substrate body can be comprised of a hard metal, a cermet or a ceramic.

Preferably the ratio of the TiCN— phase, the TiOCN phase, TiC phase or TiOC phase to the further phase of ZrO₂ and/or HfO₂, should lie between 4:1 and 1:4 preferably between 2:1 and 1:1.

As has already been indicated, for example the first phase of TiCN or TiOCN also can be replaced by TiC or TiOC so that the ratio of C:N of 0.5:0.5 can be replaced by 1.0:0

The present invention encompasses also such tools in which in the TiCN-phase or TiOCN phase or TiOC phase or TiC phase, the titanium is replaced to a small proportion by Hf in the compound TiC_(x)N_(y)O_(z) with 0≦x, y, z≦1 so that less than half the titanium can be replaced by Zr or Hf. Preferably a maximum of 20%, and even more preferably a maximum of 10% of the titanium is so replaced. Such compounds can be produced for example when the gas atmosphere from which the respective phase is deposited, contains a substoichiometric amount of oxygen.

According to a further feature or variant of the invention, the two-phase layer can be provided as an intermediate layer which is disposed between TiCN and Al₂O₃ and on which a ZrCN coating is externally deposited.

To produce the tool according to the invention it is proposed that upon the sintered substrate body for the CVD deposition. of the aforementioned multiphase layer, the method according to claim 7 be used and which is characterized in that, in the gas atmosphere, apart from TiCl₄, HfCl₄ and/or ZrCl₄ and CO₂, additionally CH₃CN (acetonitrile) or C₅H₅N (pyridine) or C₆H₆ (benzene) is provided, the balance being H₂ and/or Ar. When acetonitrile is used the following simultaneous reactions run in the gas phase: 2 TiCl₄+CH₃CN+4.5 H₂→2 TiC_(0.5)N_(0.5)+CH₄+8HCl ZrCl₄+2 CO₂+2 H₂→ZrO₂+2 CO+4 HCl or 2 TiCl₄+CH₃CN+4.5 H₂→2 TiC_(0.5)N_(0.5)+CH₄+8HCl HfCl₄+2 CO₂+2 H₂→HfO₂+2 CO+4 HCl

Corresponding reactions occur when instead of acetone, pyridine is used, whereby as a reaction product a TiC_(x)N_(y)-phase will also arise. However, in the case of use of pyridine in the gas phase the C:N proportion changes from 0.5:0.5 to 0.7:0.3 and when benzene is used the proportion beocmes 1.0:0, that is in the first phase less or no nitrogen is contained.

Preferably the following gas proportions are used:

-   TiCl₄:1:4 vol. %, preferably 1:2 vol. % ZrCl₄ and/or HfCl₄:0.3 to 4     Vol. % preferably 0.5 to 2 vol. % C₅H₅N or CH₃CN or C₆H₆: 0.2 to 2     vol. % preferably 0.5 to 1 vol %. CO₂:0.1 to 3 Vol. %, preferably     0.3 to 2 vol. %.

Balance Ar and/or H₂.

The deposition temperature in a preferred application of the invention lies between 800° and 1000° C. and the gas atmosphere pressure is 5×10³ Pa to 6×10⁴ Pa.

In a concrete example, a hard metal substrate body has a hard material phase of WC and a binder phase of 6% by weight Co upon which a layer sequence of TiN—TiCN/HfO₂—TiN is deposited and for the deposition of the intermediate layer, the following gas phase composition is chosen:

-   1.4 vol. % TicC,₁, 1.4 vol. % HfCl₄, 0.8 vol. % CH₃CN, 0.5 Vol. %     CO₂, balance H₂.

The other TiN layers are respectively produced using a convention CVD coating process.

In a corresponding way on a hard metal substrate body, layer sequences of TiN—TiCN—TiCN/HfO₂—αAl₂O₃ can be deposited. It has been found surprisingly that using the multiphase intermediate layer TiCN/HfO₂ in accordance with the invention with a CVD process, stable α-Al₂O₃ can be generated.

The advantages of the invention which are described in greater detail hereinafter will be apparent from the drawing:

It shows:

FIGS. 1 to 3 respective measured lives in a bar diagram comparison.

As previously described, on a hard metal substrate body which has the form of a cutting insert of the type SNUN 120408, in the first case, a layer sequence according to the invention of TiN/TiCN/HfO₂—TiN is applied. The intermediate layer thus is comprised of two phases namely, TiCN on the one hand and HfO₂ on the other.

By comparison therewith, a substrate body of the same composition and the same type is provided with a three layer coating of TiN—TiCN—TiN. In a dry turning of a steel of the type CK45N with the parameters v_(c)=200 m/min, aρ=2.0 mm and f=0.4 mm/revolution, the life of the coating according to the invention was about 15 min whereas the life of the comparative body in accordance with the state of the art was less than 12 min.

Also by comparison with a cutting body in accordance with the coating techniques of the state of the art, with a layer sequence of TiN—TiCN—K—Al₂O₃, the coating sequence according to the invention of TiN—TiCN—TiCN/HfO₂-α-Al₂O₃ can provide a continuous cut in turn of the workpiece using a coolant/lubricant, that is a wet cut, and with a significant improvement in the life of the tool.

While with the layer sequence in accordance with the state of the art in which the intermediate TiCN layer is deposited with a deposition temperature between 800° C. and 1000° C. and the gas phase only deposits K Al₂O₃, the tool has a useful life of only six minutes, whereas the life with the layer sequence in which between the TiCN layer and the Al₂O₃ layer a two phase intermediate layer of TriCN and HfO₂ has been interposed, the life is substantially greater. This intermediate layer allows, at the same process conditions, the deposition of α-Al₂O₃. The life of the tool is 9 minutes which is a 50% improvement. In the composition tests the workpiece was a cast body of GG25 and the cutting insert was of the type CNMG120412-5 and the following turning parameters were used: v_(c)=450 m/min, aρ=2.5 mm and f=0.315 mm/revolution.

As can be seen from FIG. 3, the coating according to the invention also provides in wet turning with a continuous cut a significant improvement in the life of the tool. On a substrate body of the same composition as type CNMG120412-5, a layer sequence of the composition TiN—TiCN(MT)-TiCN/HfO₂-α-Al₂O₃ was applied in a first case and in the second case a layer sequence of TiN—TiCN (MT)K—Al₂O₃—ZrCN was applied.

Both cutting inserts were used for the turning of a cast iron body of the type GG25 with the following machining parameters v_(c)=400 m/min, aρ=2.5 mm, f=0.315 mm/revolution.

The life of the insert which was made with the layer composition according to the invention in which a two-phase intermediate layer TiCN/HfO₂ was introduced, was 12.5 min whereas the cutting insert according to the state of the art had a life of 10.2 min.

The aforedescribed test results show clearly that both with dry turning and also with turning in a wet state, significant improvements in the life of the tool can be achieved. 

1. A tool, especially a cutting tool comprised of a substrate body upon which at least one coating or layer is deposited by means of CVD, characterized in that the single deposited coating or at least one of the layers has apart from a TiCN phase or a TiOCN phase or a TiOC phase or a TiC phase, a further phase comprised of ZrO₂ and/or HfO₂.
 2. The tool according to claim 1 characterized in that the further phase is present in monoclinic and/or tetragonal form.
 3. The tool according to claim 1 characterized in that on the coating or layer which contains ZrO₂ and/or HfO₂ as the further phase, Al₂O₃ is deposited, preferably as an outer coating and preferably further as α-Al₂O₃.
 4. The tool according to claim 1, characterized in that the substrate body is comprised of a hard metal, a cermet or a ceramic.
 5. The tool according to claim 1, characterized in that the ratio of the TiCN phase, TiOCN phase, TiC phase or TiOC phase to the further phase lies between 4:1 and 1:4, preferably between 2:1 and 1:2.
 6. The tool according to claim 1, characterized in that in the TiCN phase, or TiOCN phase, or TiOC phase or TiC phase, the titanium is replaced to a small proportion by Zr and/or Hf.
 7. The tool according to claim 1, characterized in that the two phase layer is an intermediate layer between two TiN layers.
 8. A method of CVD deposition of a two phase layer upon a substrate body in accordance with claim 1, characterized in that into the gas atmosphere apart from TiCl₄, HfCl₄ and/or ZrCl₄ and CO₂, CH₃CN (acetonitrile) or C₅H₅N (pyridine) or C₆H. (benzene) are introduced, the balance being H₂ and/or Ar.
 9. The method according to claim 8 characterized by the following gas proportions: TiCl₄: 1 to 4 vol. % preferably 1 to 2 vol. % ZrCl₄ and/or HfCl₄ 0.3 to 4 vol. %, preferably 0.5 to 2 vol. % C₅H₅N or CH₃CN or C₆H₆: 0.2 to 2 vol. %, preferably 0.5 to 1 vol. %; CO₂:0.1 to 3 vol. %, preferably 0.3 to 2 vol. % balance Ar and/or H₂.
 10. The method according to claim 8 characterized in that the deposition temperature lies between 800° C. and 1000° C. and the gas atmosphere pressure lies between 5×10³ and 6×10⁴ Pa. 